This is the IP address seen by servers on the internet when you request informtaion
from them.
But keep in mind, that this is only the IP address of the machine you are working on, if you
are directly connected to the internet.
If you are sitting in your home office, then this is the IP which your internet router
got from your internet service provider.
If you are sitting in any company premises, this will most likely be the IP address of
the proxy server through which you are connected to the internet.

How it works:

The page itself is written in plain html, and the active content, which carries the
needed information, i.e.
$REMOTE_ADDR
is included into the page using server side include technology.